How can HST training build more muscle than a standard heavy lifting workout?

Example:

On an HST day, you would do a couple exercises targeting the chest, at 1 or 2 sets. While also, working the rest of the major muscle groups.

vs

My normal workout would consist of 4/5 chest exercises at 3 sets each. While also, working triceps and abs.

..So how can this small amount of chest exercise (HST) compare to the heavy workout I would do on chest day?

To me,.. it seems I would lose size from the lack of stress I'm putting on my chest.

All weight training should be "hypertrophy training." That's the entire reason for lifting. Focus on the basic compound movements and getting stronger. No need to have a "pump" workout. If all you are doing is high reps with lower weights to get a pump you aren't going to get **** in the way of damage to the muscle fibers to make your body grow. I always got a better "pump" (I really hate that word) from going heavy and trying to beat my logbook each time anyway.

One other thing to consider is that it's not the total volume of the lifts that day that are going to make you grow. I could never make it through 4-5 chest exercises unless I was going light which IMHO completely defeats the purpose. I can get 1-2 exercises going all out and then I'm done. If you still have gas in the tank after doing something like incline bench and weighted dips you didnt go heavy enough or push hard enough.